Heavy filler in golf ball cores

ABSTRACT

Two and three piece golf balls having improved rebound characteristics include cores and centers, respectively, that are comprised of polybutadiene rubber and inorganic fillers with specific gravities of about 5.4 or greater. The inorganic fillers may be selected from tungsten, bismuth, copper, bismuth oxide, nickel, cobalt, iron, steel, tin, chromium, zinc, bismuth subcarbonate, cupric oxide, barium tungstate, cuprous oxide or ferrous oxide.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] A claim of benefit is made to U.S. Provisional Application Ser.No. 60/093,229 filed Jul. 17, 1999, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates generally to compositions for golf balls.More specifically, the invention relates to fillers for golf ballcenters and cores.

[0004] 2. Description of the Related Art

[0005] One of the parameters of golf ball performance that receivesgreat attention is flight distance. Although there are a variety offactors that influence a golf ball's flight distance, perhaps the mostimportant factor relates to the rebound characteristics of the ballwhich is dictated in large part by the materials used to construct thegolf ball.

[0006] As is well known in the industry, there are a number of differenttypes of golf balls. The predominant varieties are a two-piece and athree-piece golf ball. A two piece golf ball is typically constructedwith a solid core and a cover. A three-piece ball is typically a threadwound solid center with a cover. Within these two broad categories arenumerous variations such a liquid filled centers for three-piece balls.Regardless of the particular golf ball type, all golf balls have reboundcharacteristics that are dictated by the materials and construction typeutilized.

[0007] To conform to United States Golf Association (“U.S.G.A.”)guidelines and regulations, golf balls have to be constructed to meetspecific weight requirements. When a golf ball core or centercomposition is below specified weight requirements, one of thetechniques used to increase weight is to add fillers to the centers andcores of three-piece golf balls and two-piece golf balls, respectively.Conventional fillers used include calcium carbonate (specific gravity of2.73), barium sulfate (sp. gr. of 4.3) and zinc oxide (sp. gr. 5.6).Although these materials can be effectively used to increase the weightof a golf ball, the inevitable volume occupied by these materials whenincorporated into a center or core results in a reduction in the mpolymer/rubber content of the center or core. By extending the rubberwith fillers or reducing the polymer/rubber content, the coefficient ofrestitution of the resulting golf ball is reduced which translates intoreduced flight distance.

[0008] The compression of a golf ball is a measure of the deflection ofthe golf ball under a load of 200 lbs. The Professional Golf Association(PGA) measures compression as (0.180″- deflection)×100. Typically, thelower the PGA compression the softer the golf ball. The softer golf ball(with a softer core and/or cover) exhibits better feel, click and spincharacteristics when compared with a high compression golf ball.

[0009] An additional detrimental side effect of high stiffness contentis that a high loading of fillers stiffens the rubber compound andincreases the compression of the core or center while reducing theresilience properties.

[0010] It has now been discovered that the incorporation of high densitymaterials such as tungsten into cores and centers can be used to meetgolf ball weight requirements without significantly reducing thecoefficient of restitution or increasing the compression of the golfball produced. In some instances, the opposite effect has been observed.

[0011] It is thus an object of the invention to provide a golf ballcenter or core composition that uses high specific gravity fillers inorder to maintain the weight of a conventional golf ball core or centerhaving a lower compression without significantly compromising theresilience characteristics of the golf ball in which such a center orcore is incorporated. A further object is to meet the USGA golf ballweight requirements without increasing the golf ball compression.

SUMMARY OF THE INVENTION

[0012] The invention described herein relates to the addition of highdensity inorganic powders of metals and oxides that can be used toincrease the weight of a center for a two-piece golf ball and the coreof a three-piece wound golf ball without significantly compromising therebound characteristics of the golf ball produced. The fillers used havea high specific gravity of about 5.4 and higher.

[0013] These objects and features of the present invention will beapparent from a review of the drawings and a reading of the followingdetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a cross section of a three-piece golf ball according toone embodiment of the invention.

[0015]FIG. 2 is a cross section of a two-piece golf ball according toone embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] As is well known in the art, fillers can be incorporated intogolf ball cores and centers to increase the weight of the resulting golfball. It has now been discovered that the utilization of high densityfillers having specific gravities of about 5.4 or greater can be used toincrease the weight of a golf ball center 1 (as shown in FIG. 1), orcore 1 a (as shown in FIG. 2) without significantly reducing the reboundcharacteristics of the resulting golf ball which further comprises cover2.

[0017] The following table contains a list of high density inorganicelements that meet the aforementioned criteria. The list is provided byway of illustration and not limitation. The key criteria is that thefiller material must have a specific gravity of at least about 5.6.TABLE 1 Inorganic Element Specific Gravity Tungsten 19.3 Bismuth 9.8Copper 8.9 Bismuth oxide 8.9 Nickel 8.9 Cobalt 8.9 Iron/Steel 7.7 Tin7.3 Chromium 7.2 Zinc 7.1 Bismuth subcarbonate 6.9 Cupric oxide 6.4Barium tungstate 6.4 Cuprous oxide 6.0 Ferrous oxide 5.7

[0018] In one embodiment, centers or cores incorporating such fillersare prepared by dry mixing polybutadiene rubber with the filler ofchoice and other rubber vulcanizing ingredients to create the desiredblend. Mixing can be accomplished in an internal mixer such as a Banburymixer or an open mill as is well known in the art. The mixture is thensheeted and allowed to cool for preferably 8 hours minimum.

[0019] The sheeted material is then placed in a warm up mill and heatedto about between 110° F. to 160° F. The sheets are then stripped off themill of desired thickness and width and fed into an extruder. A die ofdesired geometric shape converts the sheets into extrudate which is cutinto plugs of desired weight. The plugs are then optionally fed into aduster to dust the plugs to prevent the plugs from adhering to eachother.

[0020] Next, the plugs are placed into compression molds for finalforming. For purposes of forming golf ball cores or centers, the plugsare heated under pressure in the molds to preferably at least 290° F. asis well known in the art to ensure peroxide activation. The molded coresor centers are maintained in the molds until cured. As is well known inthe art, the amount of time needed to cure the cores and centers is aproduct of the peroxide activity. The end result is a core or centerhaving the desired diameter.

[0021] The following examples are illustrative of the advantages obtainsby using high density fillers. The amounts of compound components arespecified as being parts per hundred parts by weight of rubber unlessspecified otherwise. As used herein, “high cis” shall mean a cis contentof 92% or greater. The same specific gravity was maintained for allthree compounds to give the same weight after molding of the cores. Onlypart levels of the weight enhancing filler was varied in the compound.EXAMPLE 1 A B C COMPOUND High cis polybutadiene 100 100 100 Zincdiacrylate 29.5 29.5 29.5 Zinc oxide 5 5 5 Zinc stearate 3 3 3 Coreregrind 7.5 7.5 7.5 Peroxide 2.125 2.125 2.125 Calcium carbonate (2.73)20.805 — — Zirconium dioxide (5.50) — 15.285 — Tungsten (19.3) — —12.875 Total 167.930 162.410 160.000 Compound specific gravity 1.1391.139 1.139 Volume occupied by filler (%) 5.17 1.95 0.48 CORE DATA: Size(inches) 1.54 1.54 1.54 Weight (g) 36.7 36.8 36.7 Compression (PGA) 95.789.3 83.0 Coefficient of restitution 0.695 0.697 0.702 BALL DATA: Size(inches) 1.68 1.68 1.68 Weight (g) 45.3 45.2 45.1 Compression (PGA)103.6 97.3 93.2 Coefficient of restitution 0.703 0.706 0.706 FLIGHTDATA: Driver; carry (yards) 245.5 245.7 246.3

[0022] As clearly demonstrated by the test results, the use of heavyweight fillers results in a desirable lower PGA compression and a highercoefficient of restitution relative to a core or center made with afiller having a lower specific gravity. When a filler having arelatively low specific gravity is used, inevitably more filler has tobe used to meet the desired weight range for the core or center. Theincreased amounts of filler results in the reduction of other compoundcomponents. It is this reduction that leads to the increase in PGAcompression and decrease in coefficient of restitution.

[0023] It will be appreciated that the instant specification and claimsare set forth by way of illustration and made without departing from thespirit and scope of the present invention. Having thus described myinvention, what I claim as new and desire to secure by United StatesLetters Patent is:

1. A golf ball comprising: a core comprising polybutadiene rubber and aninorganic filler having a specific gravity equal to or greater thanabout 5.6; and, a cover.
 2. The golf ball of claim 1 wherein theinorganic filler is selected from the group consisting of tungsten,bismuth, copper, bismuth oxide, nickel, cobalt, iron, steel, tin,chromium, zinc, bismuth subcarbonate, cupric oxide, barium tungstate,cuprous oxide, ferrous oxide and mixtures thereof.
 3. A golf ballcomprising: a center comprising polybutadiene rubber and an inorganicfiller having a specific gravity equal to or greater than about 5.4; athread winding layer wherein the thread winding comprises polybutadienerubber; and, a cover.
 4. A golf ball according to claim 3 wherein theinorganic filler is selected from the group consisting of tungsten,bismuth, copper, bismuth oxide, nickel, cobalt, iron, steel, tin,chromium, zinc, bismuth subcarbonate, cupric oxide, barium tungstate,cuprous oxide, ferrous oxide and mixtures thereof.